The present invention is directed toward a nickel-base alloy with superior stress rupture strength and grain size control, as well as fatigue strength and corrosion resistance.
There exists in certain industries a need for alloys which can operate under severe conditions, notably high temperature and stress. This is true, for example, with respect to gas turbine components, where current specifications require a life of greater than 50 hours at stress rupture conditions of 871.degree. C./98 MPa (1600.degree. F./14.2 ksi). The manufacturers of such components have been setting increasingly higher standards, thus requiring materials suppliers to search for better alloys while maintaining a competitive price. The strict requirements for such an alloy require that it have isothermal and cyclic oxidation resistance, carburization resistance, good thermal stability after long term exposure at intermediate temperatures, good weldability, controlled grain size, and excellent stress rupture strength.
One alloy widely used for this purpose has been Inconel.RTM. alloy 617. (Inconel is a trademark of the Inconel family of companies) Stress rupture (SRU) life for this alloy has typically been limited to approximately 47 hours at 927.degree. C./62 MPa (1700.degree. F./9 ksi). Indeed, SRU life can be extended to over 100 hours with increased annealing temperatures. However, this greater SRU life is obtained at the expense of cyclic fatigue strength, which is lowered by the increased grain size resulting from the higher anneal temperature.
It is an object of the present invention to provide a nickel-base alloy which exhibits improved stress rupture life, excellent fatigue strength through grain size control and has good corrosion resistance.